Why Andy Rubin stepped down ?

Since Andy Rubin founded Android Inc. in 2003, he has been the Android father figure. Even after the big Google acquisition in 2005, he was deeply involved in Android matters; from thinking the product through to making critical decisions and handpicking Android speakers and developer relations team.

I mean, it's clear that he has been very passionate about his product/baby.

And if you're a startupper/product guy, you know how hard it is to abandon ship. This could be due to three reasons :

1- Your product isn't doing well.

Which, obviously wasn't the case for Android; as it has been Google's biggest success since search. It's actually doing so well that the resources allocated to Android within the company, as you could guess, are quite high.

2- Misunderstanding.

This could be a valid reason; When Larry Page took over the reigns of Google after Eric Schmidt, the decisions he has made had a massive effect on Google (both culture and product wise). Many products were abandoned (this wave started with the Google Labs products and propagated very recently to Google Reader, and others), new ones were created under the Google+ social umbrella, and the company gave greater interest to UX/UI with the new unified UI.

So the question that pops up is : was there a decision that involved Android and was taken by Larry Page that didn't suit Andy Rubin ?!

Let's step back for a second.

Mozilla Corporation is working on FirefoxOS, and if we assume that FirefoxOS is a threat to Android, it could be for one simple reason: the Apps Marketplace.

With an HTML5 and APIs based mobile operating system, we can expect the FirefoxOS marketplace to boom. Millions of developers could build native HTML5 apps for FirefoxOS, which will lead to user adoption which could lead to ... FirefoxOS surpassing Android (in terms of marketshare). It's a long bet, but it could happen.

What would you do if you were a business owner ? Do the same in order to prevent the inevitable. But wait a second ... Google has Chrome. Which got ported to laptops as ChromeOS, and could easily be ported to smartphones/tablets.

Especially with assigning Android to the Chrome/Apps SVP, the move seems more like merging the branches of Chrome and Android, into a single master branch.

3- You have bigger plans elsewhere : The Google X Lab.

I won't go into the details (well, they're pretty much unknown even for Google employees). But you could look at it in Wikipedia.

Basically it's a research facility grouping some of this century's brightest minds, visionaries and sci-fi geeks (no kidding). Some of the projects that graduated from the lab are Glass and the Google Driverless Car.

Could Google be working on a bigger project that requires Andy's talents ?

From a pure business perspective, this is a long shot.

Finally ...

The only strong theory that persists is the second.

Could Google be merging Android and ChromeOS to release a more integrated/cross platform operating system spanning from mobile to desktop/laptop ?

It has to be.